The present device relates to a channel preset device.
Conventionally, with this type of channel preset device, in a case where a tuner of a phase-locked loop (PLL) system is adopted, the received frequency of the tuner is sequentially varied with regard to the respective channels on the basis of a predetermined channel plan, and a horizontal synchronizing signal which is separated from an output of the tuner at each channel frequency is first counted to determine whether a broadcasting is on the air. Here, if it is determined that a broadcasting is on the air, a determination is made as to whether or not the broadcasting signal can be pulled into a normal tuning point, and if it is possible, a determination is finally made that the broadcasting is on the air, and that channel is stored as a memory channel. On the other hand, if the horizontal synchronizing signal cannot be detected, or if it is impossible even if the horizontal synchronizing signal has been detected, a determination is made that no broadcasting is on the air, and that channel is stored as a skipped channel.
On the other hand, with a channel preset device disclosed in Japanese Utility Model Publication No. 5-78073A, a vertical synchronizing signal is separated from a tuner output, noise components included in the vertical synchronizing signal are eliminated, and the vertical synchronizing signal with the noise components thus eliminated is counted, thereby determining whether or not a normal tuned state has been obtained.
With the above-described related channel preset devices, the following problems have been encountered.
With the former device, there have been cases where even if no broadcasting is on the air, an erroneous determination can be made that the horizontal synchronizing signal has been detected due to the effect of noise or the like. Further, since the AFC pull-in processing is effected by detecting a point of change in a difference voltage corresponding to an offset of the frequency of an actual image carrier wave from a reference frequency while varying the received frequency of the tuner in finely, there have been cases where a point of change which occurs accidentally is detected, and a determination is erroneously made that a broadcasting is on the air.
On the other hand, with the latter device, since circuitry and the like for eliminating the noise components which are included in the separated vertical synchronizing signal are required, the cost has tended to become high.
The present device has been made in view of the above-described problems, and its object is to provide a channel preset device which is capable of detecting an on-air channel more reliably and storing the same without adding special circuitry and the like.
In order to achieve the above object, there is provided a channel preset device comprising:
tuner means for receiving a television broadcasting signal corresponding to a desired frequency and subjecting the television broadcasting signal to predetermined signal processing and outputting the same;
sync separation means for separating horizontal and vertical synchronizing signals from the output signal of the tuner means and outputting the same;
on-air judgement means for judging whether a broadcasting is on the air on the basis of the presence or absence of the horizontal synchronizing signal in the output signal of the sync separation means while continuously varying a received frequency of the tuner means;
tuning-point detection means for detecting a normal tuning point while varying the received frequency of the tuner means at neighboring frequencies of the frequency at which the on-air judgement means judged that the broadcasting is on the air; and
channel memory means for storing a channel corresponding to the normal tuning point when it is detected that the vertical synchronizing signal is outputted from the sync separation means at the normal tuning point detected by the tuning-point detection means.
In the device, at the time the channel memory means stores an on-air channel, the on-air judgement means continuously varies the received frequency of the tuner means. Then, the tuner means subjects the television broadcasting signal to predetermined signal processing at each received frequency and outputs the same, and the sync separation means separates horizontal and vertical synchronizing signals from an output from the tuner means and outputs the same. The on-air judgement means determines an on-air channel on the basis of the presence or absence of the horizontal synchronizing signal in the output signal of the sync separation means. Here, if the on-air judgement means detects the on-air channel, the tuning-point detection means detects a normal tuning point on the basis of the output signal of the tuner means while finely varying the received frequency of the tuner means. The channel memory means then stores a corresponding channel if it is detected that the vertical synchronizing signal in the output signal of the sync separation means at the normal tuning point.
Namely, after an on-air channel is first detected on the basis of the presence or absence of the horizontal synchronizing signal, the broadcasting signal is pulled into the normal tuning point. Then, a determination is made again as to whether or not the broadcasting is on the air on the basis of the presence or absence of the vertical synchronizing signal at that normal tuning point. If it can be determined here that a station is present, the channel is finally stored as the on-air channel. As described above, with the related technique, there have been cases where although no broadcasting is on the air, the tuning point is erroneously detected and a corresponding channel is stored due to the effect of noise or the like. In contrast, in accordance with the present invention, a determination is made as to whether or not a broadcasting is on the air on the basis of the presence or absence of the vertical synchronizing signal after detection of the normal tuning point, so that the on-air channel can be detected more reliably.
Therefore, it is possible to provide a channel preset device which is capable to detecting an on-air channel more reliably and storing the same without adding special circuitry and the like.
As the station selection system of the tuner means, it is possible to adopt various systems if they are capable of continuously varying the received frequency. For example, in a case where a voltage synthesizer system is adopted, it suffices if the tuning voltage is supplied to the tuner in such a manner as to cause the received frequency of the tuner to be varied continuously in predetermined frequency units in a television broadcast band. It goes without saying that, in such a case, the channel which is stored by the channel memory means is data such as tuning voltage value concerning an on-air channel.
Alternatively, there may be configured that: the tuner means includes a frequency synthesizer system for directly controlling a local oscillation frequency of the tuning means in order to tune the system to the desired frequency in accordance with a predetermined channel plan.
In the device, the on-air judgement means detects an on-air channel while continuously varying the received frequency of the tuner means, which has a station selection mechanism of the frequency synthesizer system, in the channel unit on the basis of a predetermined channel plan. Namely, in the frequency synthesizer system, it is possible to tune the system to a desired frequency by directly controlling the local oscillation frequency of the tuner or the like, and the broadcasting signal is received in each channel unit on the basis of a channel plan according to a broadcasting form such as normal television broadcasting or cable television broadcasting.
Accordingly, it is possible to provide a specific configuration in the case where the tuner adopts the frequency synthesizer system.
The tuning-point detection means suffices if it is capable of detecting the normal tuning point while varying the received frequency of the tuner means in vary small units, and its specific configuration is not particularly limited.
For example, there may be configured that; the output signal of the tuner means includes information concerning a difference voltage in accordance with an offset between the received frequency and an image carrier wave frequency; and the tuning-point detection means detects the normal tuning point based on the difference voltage.
In the device, the tuning-point detection means detects the normal tuning point by finely varying the received frequency of the tuner means while monitoring the difference voltage corresponding to an offset between the received frequency and the frequency of the image carrier wave based on the output from the tuner means. That is, the normal tuning point can be detected by utilizing the well-known AFC technique or the like.
The significance of detecting the presence or absence of the vertical synchronizing signal by the channel memory means at the normal tuning point detected by the tuning-point detection means lies in reducing the possibility of erroneously detecting an on-air channel, as described above. Here, it goes without saying that a determination may be made again as to whether or not a station is present by making use of the criterion of the presence or absence of the vertical synchronizing signal, and it does not necessarily mean that a determination is made again as to whether or not a station is present solely on the basis of the presence or absence of the vertical synchronizing signal.
For example, there may be configured that: the channel memory means executes:
first detection processing for detecting the horizontal synchronizing signal at the normal tuning point;
second detection processing for detecting the horizontal synchronizing signal at the normal tuning point, conducted after the lapse of a predetermined time period; and
third detection processing for detecting the vertical synchronizing signal at the normal tuning point, conducted within the predetermined time period.
In the device, when the turning-point detection means detects the normal tuning point, the channel memory means effects first detection processing for detecting the horizontal synchronizing signal from the sync separation means at that normal tuning point. Subsequently, the channel memory means similarly effects second detection processing for detecting the horizontal synchronizing signal after the lapse of a predetermined waiting time, and effects third detection processing for detecting the vertical synchronizing signal from the sync separation means during the waiting time. The channel memory means stores the channel for the normal tuning point if the synchronizing signal can be detected in each of the synchronous detection processing.
Accordingly, since the on-air channel is determined at the channel only when the synchronizing signal can be detected in each item of the detection processing. Therefore, it is possible to detect the on-air channel more reliably and store the same.